Immunoassay procedures are so commonly used as to make unnecessary elaborate discussion of the topic in general. In is well understood that a variety of formats can be used, generally involving the conjugation of an immunoglobulin or fragment thereof to a solid support, followed by specific binding of the antigen and labeling the supported conjugate in some manner. Alternative protocols permit, for example, the antigen to be bound to the support, or the analyte to compete with its labeled counterpart. There are also immunoassays which do not involve solid supports but precipitate the immunocomplexes.
Recently, assays have been constructed wherein the immunoglobulin which is specific for analyte is embedded in a porous membrane either physically absorbed, covalently bound, or entrapped attached to particles, and this membrane is placed in contact with an absorbent material which withdraws the sample and reagent solutions through the membrane by capillary action. (See U.S. Pat. No. 4,632,901 to Hybritech). By utilizing this capillary action, the reaction time is decreased, and the assays are more convenient. The current commercial name for this format is "ICON", evidently an abbreviation of "immunoconcentration".
One disadvantage of the ICON configuration is that the use of capillary action to draw the materials through the membrane, in addition to limiting the volumes that can be used, and confining the test to individual samples, requires that the absorbent membrane and housing be discarded after each test. This increases the cost of the test, and limits sensitivity to analytes whose concentration in the test solution is sufficient to accommodate the volume requirements.
The present invention remedies these disadvantages by providing a disposable means for drawing the sample through the membrane, by providing a mechanism for utilizing arbitrary amounts of sample volume, and by providing the opportunity for simultaneous multiple sample development.